This invention relates to integrated circuits; and more particularly, it relates to modules for packaging and electrically interconnecting multiple integrated circuit chips.
Conventionally, integrated circuit chips are separately encapsulated in ceramic or plastic packages from which input/output pins extend. These packages are then electrically interconnected to form larger modules by mounting them on a printed circuit board. There, electrical conductors that are etched from copper foil selectively interconnect the input/output pins.
However, a problem with packaging and electrically interconnecting chips in the above fashion is that too much space is occupied. This is because the input/output pins to each chip plus the encapsulant around each chip plus the conductors on the printed circuit between the chips take up as much or more space than the chips themselves.
To avoid this problem, multiple integrated circuit chips have been mounted on a semiconductor wafer (substrate) that is patterned with thin film conductors to interconnect the chips. Bump leads, which carry signals to and from the chips, are provided on the chips; and they attach to bonding pads on the wafer.
However, by packaging chips on a semiconductor wafer in the above fashion, several new problems occur. Firstly, a semiconductor wafer is very brittle, and thus it can easily crack. Also, metal filled via holes cannot be formed through the wafer; so signal leads from the wafer must be routed off the side of the wafer rather than through the bottom of the wafer where they would take less space. Further, no voltage planes or ground plane can be provided inside of the wafer.
These problems, it has been observed by the present inventor, could be overcome if it were possible to use co-fired alumina ceramic, rather than a semiconductor wafer, as the substrate for holding the integrated circuit chips. And, a conceptual drawing of such an integrated circuit package has been published by the present inventor in the IEEE Transactions on Components, Hybrids, and Manufacturing Technology, December, 1984. However, it has since been discovered by the present inventor that the published conceptual integrated circuit package has some serious operational problems. In particular, co-fired ceramic is a porous material; and the pores are too large to enable thin film conductors to be patterned on the ceramic surface without causing numerous shorts and open circuits to occur in them. These shorts and open circuits are described herein in greater detail in conjunction with FIGS. 4A, 4B, 5, and 6.
Accordingly, a primary object of the invention is to provide a module for electrically interconnecting multiple integrated circuit chips in which all of the above problems are overcome.